Photoperiodic conditions as a factor modulating leptin influence on pro-inflammatory cytokines and their receptors gene expression in ewe’s aorta

Influence of Leptin on the Secretion of Growth Hormone in Ewes under Different Photoperiodic Conditions

Leptin is an adipokine with a pleiotropic impact on many physiological processes, including hypothalamic-pituitary-somatotropic (HPS) axis activity, which plays a key role in regulating mammalian metabolism. Leptin insensitivity/resistance is a pathological condition in humans, but in seasonal animals, it is a physiological adaptation. Therefore, these animals represent a promising model for studying this phenomenon. This study aimed to determine the influence of leptin on the activity of the HPS axis. Two in vivo experiments performed during short- and long-day photoperiods were conducted on 12 ewes per experiment, and the ewes were divided randomly into 2 groups. The arcuate nucleus, paraventricular nucleus, anterior pituitary (AP) tissues, and blood were collected. The concentration of growth hormone (GH) was measured in the blood, and the relative expression of GHRH, SST, GHRHR, SSTR1, SSTR2, SSTR3, SSTR5, LEPR, and GH was measured in the collected brain structures. The study showed that the photoperiod, and therefore leptin sensitivity, plays an important role in regulating HPS axis activity in the seasonal ewe. However, leptin influences the release of GH in a season-dependent manner, and its effect seems to be targeted at the posttranscriptional stages of GH secretion.

The Effect of Leptin on the Blood Hormonal Profile (Cortisol, Insulin, Thyroid Hormones) of the Ewe in Acute Inflammation in Two Different Photoperiodical Conditions

As a day animal with sensitivity to inflammation similar to that of humans, the sheep may highly outperform the rodent model in inflammation studies. Additionally, seasonality makes sheep an interesting model in endocrinology research. Although there are studies concerning inflammation’s influence on leptin secretion and vice versa, a ewe model, with its possible ‘long-day leptin resistance’, is still not examined enough. The present study aimed to examine whether leptin may modulate an acute inflammation influence on plasma hormones in two photoperiodical conditions. The experiment was conducted on 48 ewes divided into four groups (control, lipopolysaccharide (LPS), leptin, LPS + leptin) during short and long days. Blood sampling started 1 hour before and continued 3 h after LPS/saline administration for further hormonal analysis. The results showed that the photoperiod is one of the main factors influencing the basal concentrations of several hormones with higher values of leptin, insulin and thyroid hormones during long days. Additionally, the acute inflammation effect on cortisol, insulin and thyroid hormones was photoperiod-dependent. The endotoxemia may also exert an influence on leptin concentration regardless of season. The effects of leptin alone on hormone blood concentrations are rather limited; however, leptin can modulate the LPS influence on insulin or thyroxine in a photoperiod-dependent way.

The Effect of Photoperiodic Conditions on GnRH/LH Secretion in Ewes

Simple Summary

During the course of evolution, animals have evolved biological rhythms that are associated with changes in the lighting and temperature of their environment. Females in most breeds of sheep are seasonal breeders, with ovulatory cycles occurring in the autumn and winter and anovulation in the spring and summer. Secretion of gonadotropin releasing hormone and luteinizing hormone, the main hormones regulating reproduction in females, displays a circadian pattern; however, data concerning the day/night differences in their secretion in ewes are incomplete. The aim of the undertaken study was to determine the day/night differences in the secretion of gonadotropin releasing hormone and luteinizing hormone in follicular phase and anestrous ewes. It was demonstrated that secretion of investigated hormones is subject to diurnal and seasonal changes. The observed reduction in luteinizing hormone release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase. It could be concluded that the nocturnal suppression of luteinizing hormone secretion in follicular phase ewes may be a mechanism moving this hormone surge to the early morning.

Abstract

Secretion of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) displays a circadian pattern. Data concerning differences in daily GnRH/LH secretion during different seasons in sheep are fragmentary. The aim of the study was to determine day/night differences in GnRH/LH secretion in the follicular phase and in the anestrous ewes. The studies were performed on Blackhead ewes (n = 24). Ewes from each season were divided into two groups of six animals (day and night group). The animals were euthanized 5 h after sunset or 5 h after sunrise and blood was taken to determine LH and melatonin concentrations. In the hypothalamus, the expression of GnRH and gonadotropin releasing hormone receptor (GnRHR) was determined. In the anterior pituitary, the expression of mRNA encoding subunit β of LH (LHβ) and GnRHR was assayed. Our study showed that GnRH/LH secretion is subject to diurnal and seasonal changes. The observed reduction in LH release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase, when the processes occurring at the hypothalamus are more equivocal. It could be concluded that the nocturnal suppression of LH secretion in follicular phase ewes may be a mechanism moving the LH surge to the early morning.

Photoperiod alters the choroid plexus response to LPS-induced acute inflammation in EWES

This study determined the influence of photoperiod on the expression of toll-like receptor 2 and 4 (TLR2 and TLR4), interleukin 1□ (IL1B), IL-1 receptor type I (IL1R1) and II (IL1R2), interleukin 6 (IL6), the IL-6 receptor (IL6R) and signal transducer (IL6ST), tumor necrosis factor α (TNF), and TNF□ receptor type I (TNFRSF1A) and II (TNFRSF1B) in the choroid plexus (ChP) of ewes with lipopolysaccharide (LPS)-induced acute inflammation. Under short-days (SD, n = 12, anestrous) and long-days (LD, n = 12, synchronized follicular phase), ewes were treated with saline or LPS. Compared to LD conditions, the ewes under SD were characterized by a greater (P<0.05) area under the curve (AUC) of cortisol in the LPS-treated group and by a lower (P<0.05) AUC of prolactin in the saline-treated group. Under both photoperiods, LPS increased (P<0.05) the expression of all examined genes except for TNFRSF1B (only under SD), TNF and TNFRSF1A (no stimulation), and IL6R (decreased (P<0.05) under SD). The LPS-induced increases in TLR2, TLR4, IL1B and its receptors, IL6 and TNFRSF1B were higher (P<0.05) under SD than LD. TLR4 was positively correlated with IL1B and IL6 in both saline- (r2 = 0.64, P<0.01 and r2 = 0.52, P<0.01) and LPS-treated (r2 = 0.81, P<0.0001 and r2 = 0.51, P<0.001) ewes. IL1B (r2 = 0.56, P<0.01 and r2 = 0.77, P<0.0001) and IL6 (r2 = 0.77, P<0.005 and r2 = 0.35, P<0.05) were positively correlated with TLR2 in saline- and LPS-treated ewes, respectively. This indicates that in ewes, the ChP response to acute systemic inflammation is dependent upon the photoperiod with stronger effects being observed under SD. Our results also suggest that gonadal hormones altering TLR4 signaling events are involved in the photoperiodic modulation of the ChP response to LPS. Further experiments are required to explain the mechanism involved in this phenomenon.

Anandamide Influences Interleukin-1β Synthesis and IL-1 System Gene Expressions in the Ovine Hypothalamus during Endo-Toxin-Induced Inflammation

Simple Summary

Pro-inflammatory cytokines are considered to be one of the most important mediators affecting the function of central nervous system during an immune/inflammatory challenge. It was found that in acting on different hypothalamic nuclei, pro-inflammatory cytokines influence the centrally regulated processes including reproduction. Recently, it has been shown that the endocannabinoid system and endogenous cannabinoids may attenuate the inflammatory response. Therefore, in our study we examined the influence of anandamide, one of the earliest known endocannabinoids, on the synthesis of interleukin (IL)-1β and IL-1 system gene expressions in the hypothalamic structures involved in gonadotropin-releasing hormone (GnRH)-ergic activity, and thus the central control of reproduction, during immune stress induced by endotoxin injection. It was found that anandamide inhibited lipopolysaccharide (LPS)-stimulated synthesis of IL-1β in the hypothalamus, likely affecting posttranscriptional levels of this cytokine synthesis. Anti-inflammatory effect of anandamide at the level of central nervous system might also result from its stimulating action on IL-1 antagonist and IL-1 type II receptor gene expression. This study suggests the potential of endocannabinoids and/or their metabolites in the inhibition of inflammatory process at the level of the central nervous system, as well as their usefulness in the therapy of inflammation-induced neuroendocrine disorders, but further detailed research is required to investigate this issue.

Abstract

This study evaluated the effect of anandamide (AEA) on interleukin (IL)-1β synthesis and gene expression of IL-1β, its type I (IL-1R1) and II (IL-1R2) receptors, and IL-1 receptor antagonist (IL-1RN) in the hypothalamic structures, involved in the central control of reproduction, during inflammation. Animals were intravenously (i.v.) injected with bacterial endotoxin-lipopolysaccharide (LPS) (400 ng/kg) or saline, and two hours after LPS administration., a third group received i.v. injection of AEA (10 μg/kg). Ewes were euthanized one hour later. AEA injection (p < 0.05) suppressed LPS-induced expression of IL-1β protein in the hypothalamus. The gene expression of IL-1β, IL-1RN, and IL-1R2 in the hypothalamic structures was higher (p < 0.05) in animals treated with both LPS and AEA in comparison to other experimental groups. AEA administration did not influence LPS-stimulated IL-1R1 gene expression. Our study shows that AEA suppressed IL-1β synthesis in the hypothalamus, likely affecting posttranscriptional levels of this cytokine synthesis. However, anti-inflammatory effect of AEA might also result from its stimulating action on IL-1RN and IL-1R2 gene expression. These results indicate the potential of endocannabinoids and/or their metabolites in the inhibition of inflammatory process at the level of central nervous system, and therefore their usefulness in the therapy of inflammation-induced neuroendocrine disorders.

Photoperiod Affects Leptin Action on the Choroid Plexus in Ewes Challenged with Lipopolysaccharide-Study on the mRNA Level

The ovine choroid plexus (ChP) expresses the long isoform of the leptin receptor, which makes this structure a potential target for leptin action. In sheep, leptin concentration in plasma is higher during long days (LD) than short days (SD). This study evaluates the influence a of photoperiod on leptin impact on the gene expression of Toll-like receptor 4 (TLR4), proinflammatory cytokines (IL1B, IL6), their receptors (IL1R1, IL1R2, ILRN, IL6R, IL6ST) and inflammasome components necessary for pro-IL-1β activation (NLRP3, PYCARD, CASP1), chemokine (CCL2), leptin receptor isoforms (LEPRa, LEPRb) and a suppressor of cytokine signalling (SOCS3) in the ChP of ewes treated or not with lipopolysaccharide (LPS). Studies were conducted on adult female sheep divided into four groups (n = 6 in each): control, leptin (20 μg/kg), LPS (400 ng/kg), and LPS and leptin injected under SD and LD photoperiods. The leptin alone did not affect the gene expression but in co-treatment with LPS increased (p < 0.05) IL1B but only during SD, and SOCS3, IL1R2, IL1RN, IL6ST and CCL2 only during LD, and decreased (p < 0.05) the IL1R1 expression only during SD photoperiod. This indicates that the immunomodulatory action of leptin on the ChP is manifested only under the LPS challenge and is photoperiodically dependent.

Interplays between inflammasomes and viruses, bacteria (pathogenic and probiotic), yeasts and parasites

In recent years, scientists studying the molecular mechanisms of inflammation have discovered an amazing phenomenon - the inflammasome - a component of the innate immune system that can regulate the functional activity of effector cells during inflammation. At present, it is known that inflammasomes are multimolecular complexes (cytosolic multiprotein oligomers of the innate immune system) that contain many copies of receptors recognizing the molecular structures of cell-damaging factors and pathogenic agents. Inflammasomes are mainly formed in myeloid cells, and their main function is participation in the cleavage of the pro-IL-1β and pro-IL-18 cytokines into their biologically active forms (IL-1β, IL-18). Each type of microorganism influences particular inflammasome activation, and long-term exposure of the organism to viruses, bacteria, yeasts or parasites, among others, can induce uncontrolled inflammation and autoinflammatory diseases. Therefore, this review aims to present the most current scientific data on the molecular interplay between inflammasomes and particular microorganisms. Knowledge about the mechanisms responsible for the interaction between the host and certain types of microorganisms could contribute to the individuation of innovative strategies for the treatment of uncontrolled inflammation targeting a specific type of inflammasome activated by a specific type of pathogen.

The Impact of Photoperiod on the Leptin Sensitivity and Course of Inflammation in the Anterior Pituitary

Leptin has a modulatory impact on the course of inflammation, affecting the expression of proinflammatory cytokines and their receptors. Pathophysiological leptin resistance identified in humans occurs typically in sheep during the long-day photoperiod. This study aimed to determine the effect of the photoperiod with relation to the leptin-modulating action on the expression of the proinflammatory cytokines and their receptors in the anterior pituitary under physiological or acute inflammation. Two in vivo experiments were conducted on 24 blackface sheep per experiment in different photoperiods. The real-time PCR analysis for the expression of the genes IL1B, IL1R1, IL1R2, IL6, IL6R, IL6ST, TNF, TNFR1, and TNFR2 was performed. Expression of all examined genes, except IL1β and IL1R2, was higher during short days. The leptin injection increased the expression of all examined genes during short days. In short days the synergistic effect of lipopolysaccharide and leptin increased the expression of IL1B, IL1R1, IL1R2, IL6, TNF, and TNFR2, and decreased expression of IL6ST. This mechanism was inhibited during long days for the expression of IL1R1, IL6, IL6ST, and TNFR1. The obtained results suggest the occurrence of leptin resistance during long days and suggest that leptin modulates the course of inflammation in a photoperiod-dependent manner in the anterior pituitary.

The Influence of Photoperiod on the Action of Exogenous Leptin on Gene Expression of Proinflammatory Cytokines and Their Receptors in the Thoracic Perivascular Adipose Tissue (PVAT) in Ewes

Leptin resistance is either a condition induced by human obesity or a natural phenomenon associated with seasonality in ruminants. In the cardiovascular system, the leptin resistance state presence is a complex issue. Moreover, the perivascular adipose tissue (PVAT) appears to be crucial as a source of proinflammatory cytokines and as a site of interaction for leptin contributing to endothelium dysfunction and atherosclerosis progression. So the aim of this study was to examine the influence of the photoperiod on the action of exogenous leptin on gene expression of selected proinflammatory cytokines and their receptors in thoracic PVAT of ewe with or without prior lipopolysaccharide (LPS) stimulation. The experiment was conducted on 48 adult, female ewes divided into 4 group (n = 6 in each): control, with LPS intravenous (iv.) injection (400 ng/kg of BW), with leptin iv. injection (20 μg/kg BW), and with LPS and 30-minute-later leptin injection, during short-day (SD) and long-day (LD) seasons. Three hours after LPS/control treatment, animals were euthanized to collect the PVAT adherent to the aorta wall. The leptin injection enhanced IL1B gene expression only in the LD season; however, in both seasons leptin injection intensified LPS-induced increase in IL1B gene expression. IL1R2 gene expression was increased by leptin injection only in the SD season. Neither IL6 nor its receptor and signal transducer gene expressions were influenced by leptin administration. Leptin injection increased TNFA gene expression regardless of photoperiodic conditions. Only in the SD season did leptin treatment increase the gene expression of both TNFα receptors. To conclude, leptin may modulate the inflammatory reaction progress in PVAT. In ewe, the sensitivity of PVAT on leptin action is dependent upon the photoperiodic condition with stronger effects stated in the SD season.

Effect of Central Injection of Neostigmine on the Bacterial Endotoxin Induced Suppression of GnRH/LH Secretion in Ewes during the Follicular Phase of the Estrous Cycle

Induced by a bacterial infection, an immune/inflammatory challenge is a potent negative regulator of the reproduction process in females. The reduction of the synthesis of pro-inflammatory cytokine is considered as an effective strategy in the treatment of inflammatory induced neuroendocrine disorders. Therefore, the effect of direct administration of acetylcholinesterase inhibitor—neostigmine—into the third ventricle of the brain on the gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretions under basal and immune stress conditions was evaluated in this study. In the study, 24 adult, 2-years-old Blackhead ewes during the follicular phase of their estrous cycle were used. Immune stress was induced by the intravenous injection of LPS Escherichia coli in a dose of 400 ng/kg. Animals received an intracerebroventricular injection of neostigmine (1 mg/animal) 0.5 h before LPS/saline treatment. It was shown that central administration of neostigmine might prevent the inflammatory-dependent decrease of GnRH/LH secretion in ewes and it had a stimulatory effect on LH release. This central action of neostigmine is connected with its inhibitory action on local pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)α synthesis in the hypothalamus, which indicates the importance of this mediator in the inhibition of GnRH secretion during acute inflammation.